Hypertension (HTN) is a major health problem in the United States placing some 58 million Americans at increased risk for stroke, myocardial infarction, kidney failure, and peripheral vascular disease. African Americans are especially vulnerable to HTN, with as many as 38% of the adult Black population affected with this disorder. Although pharmacologic management of HTN is often effective, medications are not without complications and untoward side effects. Consequently, there has been a great deal of interest in the development and application of behavioral treatments for the management of HTN. The present study is a single randomized clinical trial of exercise with three long-term objectives. The first is to evaluate the efficacy of aerobic exercise in reducing blood pressure in older African American men and women with mild HTN (Systolic blood pressure (BP) 140-180 mmHg and Diastolic BP 90-105 mmHg); the second is to examine the mechanisms by which blood pressure is reduced; and the third is to investigate the effects of exercise on cognitive performance and related aspects of quality of life. Fifty-one African American subjects, aged 45 to 80, with mild HTN have been recruited through local radio, television, newspapers, community blood pressure screenings, and flyers from the Raleigh-Durham area. As of 11/96, we have had a total of 446 inquiries, 111 of which were initially eligible. Of those 111, 64 passed the screening tests but 13 withdrew before beginning the study. The remaining 51 are enrolled currently and 42 have completed the program Of the remaining 51 who entered the study, 37 (73%) are female and 14(27%) are male. We do not plan to enroll any more subjects for this study in the upcoming year. Volunteers have been randomly assigned to 4 months of moderate aerobic exercise or a waiting list control group. Subjects undergo comprehensive evaluations at baseline and at 4 months, in addition to an initial eligibility screening, consisting of a brief physical exam and blood (11 ml) and urine (10 ml) sample. Measurements of BP is obtained in the clinic, during everyday life using ambulatory blood pressure monitoring, and during physical exercise. Blood pressures are also obtained at 6 month follow-up. In order to examine potential mechanisms responsible for blood pressure changes, subjects will undergo sodium excretion studies. A blood sample (15 ml) is obtained for lipid analysis. Each subject will be instructed to collect their urine in plastic containers for 24 hours following a standard sodium load. This procedure is repeated everyday for one week. Because hypertension has been shown to be associated with measurable changes in cognitive function, which may be reversible when blood pressure is normalized, subjects complete a neuropsychological assessment battery along with psychometric testing. The information obtained from this study will have important practical significance by determining the efficacy of exercise in lowering BP in older Black men and women with mild hypertension, and by assessing the clinical importance of these changes. Moreover, the study has important scientific significance by clarifying the mechanisms that may be responsible for the BP reductions.